In a process for fabricating an array substrate of a display device, aluminum (Al) is among the metal conductive materials which have been applied firstly. With continuous increase in resolution of the display device, aluminum gradually cannot meet new requirements. The application of aluminum has been hindered due to its drawbacks of high resistivity, prone to electronmigration failure, and hillocks during preparing process. In particular, with increase in resolution of the display device, both the wiring density and the wiring length per area increase, and aluminum is not suitable for fabricating the current display device.
To solve the above problem, copper (Cu) is applied as conductive material in the prior art. Cu has low resistivity (of 1.7 μΩ·cm, while Al has resistivity of 2.7 μΩ·cm), and has acceptable responding rate. Cu enables to form wirings or electrodes with reduced width to decrease loss. Cu can improve the wiring density, which facilitates realizing a display device with high resolution. However, as a conductive material, Cu has the following problems. Cu has strong diffusion ability, and wirings or electrodes made from Cu tend to be oxidized in an environment below 200° C., which may lead to display device defect or display abnormal. For example, in case a gate of the thin film transistor is made from Cu, Cu atoms may permeates in an active layer of the thin film transistor, which leads to function failure of the thin film transistor, and further leads to display device defect or display abnormal. For example, the gate of the thin film transistor made from Cu tends to be oxidized in an environment below 200° C. Once oxidized, the gate may lead to significant Mura defect in the display device, which leads to display device defect or display abnormal.